What distinguishes Bipolar II from Bipolar I disorder?

Bipolar II disorder is distinguished from Bipolar I disorder primarily by the presence of hypomanic episodes alongside depressive episodes. In Bipolar II, individuals experience at least one hypomanic episode (a milder form of mania that does not involve the extreme dysfunction seen in full-blown manic episodes) and at least one major depressive episode. This combination is critical in the diagnosis, as it indicates a less severe form of the disorder compared to Bipolar I, where full manic episodes are required.

The definition of hypomania involves a distinct change in mood and functioning that is observable by others, but it does not lead to the significant impairment in social or occupational functioning that a full manic episode would. The depressive episodes in Bipolar II can be severe and debilitating, making the combination of these two types of episodes particularly defining of the disorder. Understanding this distinction is essential for diagnosis and treatment, as it affects management strategies and patient outcomes.